In various mechanical devices, and particularly within automatic vehicle transmissions, specialized overrunning or one-way clutches are used to produce a one-way driving connection between the input and output members of the transmission. In particular, a one-way clutch has a pair of members, races, or plates capable of transmitting torque when the rotation of one plate with respect to the other is in one direction, with the clutch “overrunning” or freewheeling when the rotational direction is reversed.
The relative shape and/or orientation of the plates may vary depending on the particular clutch design. Certain one-way clutches have input and output races or plates that are oriented in a radially-concentric manner with respect to each other. Alternately, the confronting or mating faces of the plates have a planar orientation or relationship. The mechanical means used to lock a typical one-way clutch are varied, but commonly consist of torque-transmitting elements such as rollers, sprags, rockers, or struts that are positioned between the plates. Depending on the particular type or style of one-way clutch and the direction of rotation, each plate may contain unique surface features suitable for engaging one or more of the struts in order to selectively enable various clutch operating modes.
In a basic one-way clutch, the operating mode is determined by the direction of the torque being applied to an input race or plate of the clutch. However, the increased complexity of power transmitting mechanisms has led to a class of selectable one-way clutches. A selectable one-way clutch or SOWC is similar to a one-way clutch in operation, as described above. As the name implies, a SOWC is capable of producing a driving connection between the input and output plates in one or both rotational directions, and/or is able to freewheel in one or both rotational directions as needed. In a conventional SOWC, one of the two plates is indexed or grounded to a stationary member, such as a transmission case or center support, and therefore can be less than optimal when used in certain applications.